Regional sea level allowances along the world coast-line
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Sea level changes as a result of climate change. For projections we take ocean mass changes and volume changes into account. Including gravitational and rotational fingerprints these provide regional sea level changes. Hence, we can calculate sea-level rise patterns based on Coupled Model Intercomparison Project Phase 5 (CMIP5) projections. The variability around the mean state,originating from the climate models, is taken into account by using the concept of allowances. An allowance is the height by which a coastal infrastructure must increase in order to retain the same risk of flooding events occurring due to climate change. It is computed by taking in account the mean and uncertainty of sea level change projections, as well as the variability of extreme sea levels caused by i.e. tides and waves. Existing sets of allowances are based on tide gauges data records, which are spatially limited. Here we used data from a hydrodynamical model, including variability caused by tides and storm surges. Results show the need for more than 1 meter-allowances for most of coastline, with an increasing trend towards the equator. As a second step, changes in global significant wave height maxima towards the end of the century are computed and implemented. This leads to an increase of allowances mostly in high latitude ocean locations. Moreover, in the case of not including allowances in their coastal infrastructure, more than 70% of the studied locations worldwide will be strongly affected by a large increase in their flooding frequency.